The present invention relates to a catalyst for use in the production of aromatic hydrocarbons and a process for preparing the same. More specifically, it relates to a halogen-containing catalyst such as one or more halogen components and a platinum supported on L type zeolite catalyst in which the halogen amount distribution is uniform and a cracking activity can be reduced, and a process for preparing the catalyst.
Heretofore, as a catalyst which can be used to manufacture aromatic hydrocarbons by aromatizing non-aromatic hydrocarbons such as aliphatic hydrocarbons, platinum-alumina catalysts have been used. However, such catalysts have a drawback that hydrocarbons having 6 or 7 carbon atoms cannot efficiently be converted into aromatic hydrocarbons.
In order to solve such a problem, a catalyst in which platinum is supported on an L type zeolite has been suggested in Japanese Patent Publication No. 57408/1983, and afterward, with regard to the L type zeolite, various methods have been suggested for the improvement of an activity, a selectivity, a catalyst life and the like, or for the simplification of a catalyst preparation method.
For example, there have been suggested (1) a catalyst in which the L type zeolite supporting a metal in the group VIII has been subjected to an oxychlorination treatment to thereby improve a catalytic activity and a catalyst life (Japanese Patent Application Laid-open No. 168539/1985), (2) a catalyst treated with a solution comprising a platinum solution and a non-platinum metal salt in order to uniformly disperse and support platinum (Japanese Patent Application Laid-open No. 138539/1986), (3) a catalyst in which platinum is supported on an L type zeolite treated with a halogen-containing compound (Japanese Patent Application Laid-open No. 57653/1987), (4) a catalyst in which an L type zeolite supporting platinum is treated with a halogen-containing compound (Japanese Patent Application Laid-open No. 91334/1988), and (5) a catalyst obtained by a simple preparation method which comprises simultaneously supporting and treating a platinum component and one or more halogen components on an L type zeolite (Japanese Patent Application Laid-open No. 49936/1993).
However, the catalysts of the above-mentioned (1) to (5) have some problems in a practical use thereof, and in all of these catalysts, a cracking activity is high. In consequence, an aromatic selectivity is not sufficient.
The present invention has been developed under the above circumstances. That is to say, an object of the present invention is to provide a catalyst for use in the manufacture of aromatic hydrocarbons in which the halogen amount distribution in the catalyst is uniform, so that a cracking activity can be reduced.
Another object of the present invention is to provide a process for preparing the above-mentioned catalyst.
The present inventors have intensively researched with the intention of developing, as a catalyst for the manufacture of aromatics, a practical catalyst which can solve the problems of the above-mentioned conventional catalysts and in which a cracking activity can be reduced, and as a result, it has been found that when a water evaporation rate is retarded in a drying step in the preparation of the catalyst, the catalyst in which a halogen amount distribution in the catalyst is uniform can be obtained, so that the object of the present invention can effectively be achieved. The present invention has been completed on the basis of this knowledge.
That is to say, a first aspect of the present invention is directed to a halogen-containing catalyst which contains one or more halogen components and in which the halogen amount distribution in the catalyst is uniform, particularly, a halogen-containing catalyst wherein, in a drawing showing a relation between a sectional width direction distance (x: a distance from one catalyst surface) and an X-ray intensity (I) obtained by subjecting a halogen atom on a catalyst section to a linear analysis measurement in one direction by the use of an electron probe microanalysis (hereinafter referred to as xe2x80x9cthe EPMAxe2x80x9d) device, a ratio xcex1 [{(Fxe2x88x92F0)/F} of a value (Fxe2x88x92F0) to an integrated value (F)] is 0.17 or less, and the value (Fxe2x88x92F0) is obtained by subtracting a value (F0) obtained by integrating an X-ray intensity (I0) of a tangent of a curve at the minimum and smallest value of the curve indicating the X-ray intensity with respect to x between one catalyst surface and the other catalyst surface, from the value (F) obtained by integrating the above mentioned I with respect to x between the surfaces.
A second aspect of the present invention is directed to a process for preparing a halogen-containing catalyst which comprises the steps of supporting one or more halogen components on a carrier, particularly an L type zeolite, and then drying it at a water evaporation rate of 15% by weight/hour or less.